The present invention relates to electric or gas furnaces and electric heat pump (heating) systems in heating mode.
Heating consumption accounts for 41% of total residential energy use in the United States as reported by the US Energy Information Agency Residential Energy Consumption Survey in 2005. Known central heaters are controlled by a thermostat which turns on a heater ventilation fan after a brief delay following turning on a heat source, and turns off the heater ventilation fan after variable temperature based delay or a fixed time delay following turning off the heat source. Unfortunately, maintaining a low heater ventilation fan speed often results in increased heat soak within the central heating unit and the portion of the heat generated by the heat source is lost to the environment increases the longer the central heating element is on at the low heater ventilation fan speed. Further, the amount of heat soak increases as the central heating unit is operated for longer periods of time leaving significantly higher temperature air (i.e., 110 to 200° F.) in the heat exchanger after the heater ventilation fan is turned off and a portion of this heat is also lost to the environment after the heat source and the heater ventilation fan are tuned off.